171 lines
6.8 KiB
HTML
171 lines
6.8 KiB
HTML
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<html>
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<head>
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<title>ActiveMQ Artemis JMS Multiple Failover using Replication Example</title>
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<link rel="stylesheet" type="text/css" href="../common/common.css" />
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<link rel="stylesheet" type="text/css" href="../common/prettify.css" />
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<script type="text/javascript" src="../common/prettify.js"></script>
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</head>
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<body onload="prettyPrint()">
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<h1>JMS Multiple Failover using Replication Example</h1>
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<p>This example demonstrates three servers coupled as a live-backup-backup group for high availability (HA) using replication, and a client
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connection failing over from live to backup when the live server is crashed and then to the second backup once the new live fails.</p>
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<p>For more information on ActiveMQ Artemis failover and HA, and clustering in general, please see the clustering
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section of the user manual.</p>
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<h2>Example step-by-step</h2>
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<p><i>To run the example, simply type <code>mvn verify -Pexample</code> from this directory</i></p>
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<p>In this example, the live server is server 1, and the backup server is server 0</p>
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<p>The connection will initially be created to server1, server 1 will crash, and the client will carry on
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seamlessly on server 0, the backup server.</p>
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<ol>
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<li>Get an initial context for looking up JNDI from server #0.</li>
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<pre class="prettyprint">
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initialContext = getContext(0);
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</pre>
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<li>Look up the JMS resources from JNDI on server #0.</li>
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<pre class="prettyprint">
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Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");
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ConnectionFactory connectionFactory = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");
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</pre>
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<li>Create a JMS Connection</li>
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<pre class="prettyprint">
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connection = connectionFactory.createConnection();
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</pre>
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<li>Create a client acknowledged Session</li>
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<pre class="prettyprint">
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Session session = connection.createSession(false, Session.CLIENT_ACKNOWLEDGE);
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</pre>
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<li>Start the connection to ensure delivery occurs</li>
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<pre class="prettyprint">
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connection.start();
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</pre>
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<li>Create a JMS MessageProducer</li>
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<pre class="prettyprint">
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MessageProducer producer = session.createProducer(queue);
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</pre>
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<li>Create a JMS MessageConsumer</li>
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<pre class="prettyprint">
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MessageConsumer consumer = session.createConsumer(queue);
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</pre>
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<li>Send some messages to server #0, the live server</li>
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<pre class="prettyprint">
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for (int i = 0; i < numMessages; i++)
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{
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TextMessage message = session.createTextMessage("This is text message " + i);
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producer.send(message);
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System.out.println("Sent message: " + message.getText());
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}
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</pre>
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<li>Receive and acknowledge a third of the sent messages</li>
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<pre class="prettyprint">
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TextMessage message0 = null;
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for (int i = 0; i < numMessages / 3; i++)
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{
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message0 = (TextMessage)consumer.receive(5000);
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System.out.println("Got message: " + message0.getText());
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}
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message0.acknowledge();
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</pre>
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<p>When server #0 crashes, the client automatically detects the failure and automatically
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fails over from server #0 to server #1 (in your real program you wouldn't need to sleep).
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</p>
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<li>Acknowledging the 2nd third of the sent messages will fail as failover to the backup server has occurred</li>
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<pre class="prettyprint">
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try
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{
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message0.acknowledge();
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}
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catch (JMSException e)
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{
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System.err.println("Got exception while acknowledging message: " + e.getMessage());
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}
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</pre>
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<li>Consume again the 2nd third of the messages again. Note that they are not considered as redelivered.</li>
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<pre class="prettyprint">
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for (int i = numMessages / 3; i < (numMessages / 3) * 2; i++)
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{
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message0 = (TextMessage)consumer.receive(5000);
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System.out.printf("Got message: %s (redelivered?: %s)\n", message0.getText(), message0.getJMSRedelivered());
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}
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message0.acknowledge();
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</pre>
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<p>now we Kill server #1 and wait for the server #2 to take over the responsibilities.</p>
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<li>Acknowledging the 3rd third of the sent messages will fail as failover to the backup server has occurred</li>
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<pre class="prettyprint">
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try
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{
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message0.acknowledge();
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}
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catch (JMSException e)
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{
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System.err.println("Got exception while acknowledging message: " + e.getMessage());
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}
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</pre>
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<li>Consume again the 3rd third of the messages again. Note that they are not considered as redelivered</li>
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<pre class="prettyprint">
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for (int i = (numMessages / 3) * 2; i < numMessages; i++)
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{
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message0 = (TextMessage)consumer.receive(5000);
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System.out.printf("Got message: %s (redelivered?: %s)\n", message0.getText(), message0.getJMSRedelivered());
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}
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message0.acknowledge();
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</pre>
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<li>And finally, <strong>always</strong> remember to close your resources after use, in a <code>finally</code> block. Closing a JMS connection will automatically close all of its sessions, consumers, producer and browser objects</li>
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<pre class="prettyprint">
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finally
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{
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if (connection != null)
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{
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connection.close();
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}
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if (initialContext != null)
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{
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initialContext.close();
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}
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}
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</pre>
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</ol>
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</body>
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</html>
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